Department of Surface Waters Research and Management Eawag-Swiss Federal Institute of Aquatic Science and Technology , Seestrasse 79, CH-6047 Kastanienbaum, Switzerland.
Institute of Biogeochemistry and Pollutant Dynamics, ETH Zurich , Universitätsstrasse 16, CH-8092 Zürich, Switzerland.
Anal Chem. 2015 Dec 15;87(24):11990-7. doi: 10.1021/acs.analchem.5b02424. Epub 2015 Dec 1.
A promising profiling setup for in situ measurements in lakes with potentiometric solid-contact ion-selective electrodes (SC-ISEs) and a data processing method for sensor calibration and drift correction are presented. The profiling setup consists of a logging system, which is equipped with a syringe sampler and sensors for the measurement of standard parameters including temperature, conductivity, oxygen and photosynthetically active radiation (PAR). The setup was expanded with SC-ISEs in galvanically separated amplifiers. The potential for high-resolution profiling is investigated by deploying the setup in the eutrophic Lake Rotsee (Lucerne, Switzerland), using two different designs of ammonium sensing SC-ISEs. Ammonium was chosen as a target analyte, since it is the most common reduced inorganic nitrogen species involved in various pathways of the nitrogen cycle and is therefore indicative of numerous biogeochemical processes that occur in lakes such as denitrification and primary production. One of the designs, which uses a composite carbon-nanotube-PVC-based membrane, suffered from sulfide poisoning in the deeper, sulfidic regions of the lake. In contrast, electrodes containing a plasticizer-free methacrylate copolymer-based sensing layer on top of a conducting polymer layer as a transducer did not show this poisoning effect. The syringe samples drawn during continuous profiling were utilized to calibrate the electrode response. Reaction hotspots and steep gradients of ammonium concentrations were identified on-site by monitoring the electrode potential online. Upon conversion to high-resolution concentration profiles, fine scale features between the calibration points were displayed, which would have been missed by conventional limnological sampling and subsequent laboratory analyses. Thus, the presented setup with SC-ISEs tuned to analytes of interest can facilitate the study of biogeochemical processes that occur at the centimeter scale.
本文提出了一种有前景的用于在具有电位型固相接液离子选择性电极 (SC-ISE) 的湖泊中进行原位测量的剖析设置，以及一种用于传感器校准和漂移校正的数据处理方法。该剖析设置由一个记录系统组成，该系统配备有注射器采样器和用于测量标准参数的传感器，包括温度、电导率、氧气和光合有效辐射 (PAR)。该设置通过在隔离放大器中配备 SC-ISE 进行了扩展。通过在富营养化的 Rotsee 湖 (瑞士卢塞恩) 中部署该设置，使用两种不同设计的铵感应 SC-ISE 来研究高分辨率剖析的潜力。选择铵作为目标分析物，因为它是参与氮循环各种途径的最常见的还原无机氮物种，因此可以指示湖泊中发生的许多生物地球化学过程，如反硝化和初级生产。其中一种设计使用基于复合碳纳米管-PVC 的膜，但在湖的较深、硫化物区域受到硫化物中毒的影响。相比之下，含有在导电聚合物层顶部的无增塑剂甲基丙烯酸酯共聚物基传感层的电极则没有显示出这种中毒效应。在连续剖析过程中抽取的注射器样品用于校准电极响应。通过在线监测电极电势，在现场识别出铵浓度的反应热点和陡峭梯度。在转换为高分辨率浓度剖面后，显示了校准点之间的精细尺度特征，如果采用传统的湖泊学采样和随后的实验室分析，这些特征将被忽略。因此，具有针对感兴趣分析物进行调谐的 SC-ISE 的这种设置可以促进对发生在厘米尺度的生物地球化学过程的研究。
